Every bereavement situation is different, and, as such, the amount of time off from work you need will differ from the next person. The critical thing to understand is that you should feel free from pressure to return to work prematurely.
If you are unhappy with the amount of bereavement leave you have been granted, you should discuss it with your employer. Most will be understanding and show empathy for your situation. After all, they've invested in you and will want you to get through the grieving process as smoothly as possible.
If you are unhappy with what you've received, consider talking to your employer to explain your situation better. Alternatively, you can discuss your options with the HR department.